Pumps

ABSTRACT

The invention is concerned with an air operated hydraulic pump by which compressed air can be used to provide on the one hand a supply of hydraulic fluid under high pressure for the operation of high pressure hydraulic devices and on the other hand a supply of hydraulic fluid under relatively low pressure at a relatively high rate for rapid action of hydraulic devices under light loads. To that end a pneumatic motor is used to drive two hydraulic pumps in common; one pump is of relatively large displacement and is connected to deliver hydraulic fluid to the inlet of the other pump and therethrough to an outlet, and the pressure in the large displacement pump, and hence the pressure of relatively high rate delivery, is limited to a value low in relation to the maximum pressure of delivery fluid by the second pump stage.

United States Patent Davis [451 Apr. 11, 1972 PUMPS FOREIGN PATENTS 0R APPLICATIONS [72] Inventor: Albert H. Davis, 11, Trontbeck, Close, 744,024 4/1933 France ..4l7/397 Twyford, Berkshire, England W k Filed: July7,1970 Pnmary Examiner-Robert M. al er [21] Appl. No.: 52,839

[58] Field ofSearch ..4l7/397,52l, 523,524,526, 417/283, 301, 309

[56] References Cited UNITED STATES PATENTS 3,253,775 5/1966 Jackson ..4l7/397 2,268,695 l/l942 Carlson..... 1,487,946 3/1924 Johnston ..417/397 X Attamey-Watson, Cole, Grindle & Watson [57] ABSTRACT The invention is concerned with an air operated hydraulic pump by which compressed air can be used to provide on the one hand a supply of hydraulic fluid under high pressure for the operation of high pressure hydraulic devices and on the other hand a supply of hydraulic fluid under relatively low pressure at a relatively high rate for rapid action of hydraulic devices under light loads. To that end a pneumatic motor is used to drive two hydraulic pumps in common; one pump is of relatively large displacement and is connected to deliver hydraulic fluid to the inlet of the other pump and therethrough to an outlet, and the pressure in the large displacement pump, and hence the pressure of relatively high rate delivery, is limited to a value low in relation to the maximum pressure of delivery fluid by the second pump stage.

4 Claims, 1 Drawing Figure PUMPS The invention relates to an air operated hydraulic pump.

Compressed air is readily available in most industrial premises and frequently also on contractors sites; at the same time the use of hydraulically operated devices continues to grow and a principal object of the invention is to provide apump by which compressed air can be used to provide on the one hand a supply of hydraulic fluid under high pressure for the operation of high pressure hydraulic devices and on the other hand a supply of hydraulic fluid under relatively low pressure at a relatively high rate for rapid action of hydraulic devices under light loads.

An air operated hydraulic pump in accordance with the invention comprises a relatively large displacement hydraulic pump stage; a relatively low displacement hydraulic pump stage; means connecting the output of the first mentioned stage to the second mentioned stage; a pneumatic motor arranged to drive the said pump stages in common; and means for limiting the pressure at which fluid is delivered from the first mentioned pump stage to a value related to the air pressure available for the operation of the said motor and low in relation to the maximum pressure of delivery of fluid by the second mentioned pump stage, whereby in accordance with the demand of a load connected to the outlet of the second mentioned stage fluid can be delivered under relatively low pressure at a relatively high rate and under high pressure at a relatively low rate.

The term displacement refers to the volume swept by the piston or other moving members of the respective motor or pump during each stroke or cycle of its operation.

In order that the invention may be thoroughly understood an air operated hydraulic pump in accordance with it will be described, by way of example, with reference to the accompanying sketch drawing, which shows the pump in longitudinal section.

The unit shown in the drawing operates as follows.

Compressed air from the supply source is fed to the following points:

A. Poppet Valve Chamber B. The small diameter Piston Connection C. The Relief Valve Bellows Connection Hydraulic fluid is supplied to the point D and delivered from the Connection E.

The whole operation is motivated by the supply of compressed air to the large (relatively large displacement) air cylinder 5 and then exhausting it, which sequence is controlled by the poppet valve 6 and exhaust poppet valve 7, the position of these valves being determined by the toggle spring mechanism 8 and the supply poppet valve spring 9.

The toggle spring mechanism has two fixed pivots 10A and 10B and is moved from the one over centre position to the other by the bellcrank lever 11 pivoting on the pivot 10A. Movement of the bellcrank lever 11 is brought about by the lever 12 which is pivoted on it at the pivot 13, the lever 12 being caused to move by a projection 14 on the back of the large air piston 1 and the striker 15 which is carried on the piston rod 16.

When the lever 12 is moved on its pivot 13 it moves freely at first and then strikes abutment 17A or 17B which are part of the bellcrank lever 11 thus causing the bellcrank lever 11 to move on its pivot 10A and bring a change in the position of the supply poppet valve 6 and the exhaust poppet valve 7.

As shown on the drawing with the supply poppet valve 6 open, compressed air is being fed to the large air cylinder 5 via a pipe (not shown) between point F and connection point G.

Supply air pressure is at all times on the small (relatively small displacement) air cylinder 18 tending to urge the small air piston 2 in one direction (to the left in the Figure), but when air is supplied to the large air cylinder 5 the force, due to the greater area of air piston 1, overcomes the force being exerted by the small air piston 2 causing it to move in the opposite direction (to the right in the Figure).

The movement of the piston rod 16 (to the right) causes hydraulic fluid to be drawn into the large (relatively large displacement) hydraulic cylinder 19 through the inlet valve 20 from the connection D, at the same time forcing hydraulic fluid from the small (relatively small displacement) hydraulic cylinder 21 through the delivery valve 22 and the delivery connection E.

Now many of the applications for such an hydraulic pump as described in this invention involve the movement of an hydraulic ram within an hydraulic cylinder, for instance an hydraulic jack, and the first part of the ram 5 movement is against a light load, hence the pressures required are low but the movement of the ram needs to be as rapid as possible. Hence, assuming that the operation is at the stage where only a low pressure is required, and also assuming that this low pressure is below that required to open a relief valve, with the movement of the piston rod 16 in the opposite direction to that previously described, the large fluid piston 3 displaces the fluid in the hydraulic cylinder 19 through the valve 24 and the piston rod 16, which has been formed hollow specifically to provide this facility, into the small hydraulic cylinder 21 and as the volumetric displacement of the piston 3 is many times greater than that of the piston 4 the surplus fluid is delivered through the delivery valve 22 and the connection E. When, however, fluid at the high pressure is required, the fluid surplus to that required to fill the cylinder 21 flows back into the suction (hydraulic fluid supply) line through the relief valve 23.

The relief valve 23 has been designed to be loaded by the air supply pressure acting with a bellows 25. The object of this is that the fluid pressure within the cylinder 19 is dependant on the air pressure within the cylinder 18 which is determined by the supply air pressure available and which may vary considerably. Hence, if an alternative, say a spring loaded relief valve, was used and this was set too high, then a position of stall may be encountered due to the reduced air line pressure. Alternatively, if a spring loaded relief valve was set too low, efficiency would be lost as too large a volume of fluid would be by-passed.

The pump thus described in accordance with this invention displays the following features:

1. The pump is capable of delivering a large volume of fluid at a low pressure and a small volume of fluid at a high pressure.

2. It has a simple pneumatic valve operation.

3. The high pressure fluid delivery is regulated automatically according to the varying air line pressure.

Iclaim:

1. An air operated hydraulic pump comprising: a relatively large displacement air cylinder and a piston movable therein; inlet and exhaust valve mechanism arranged to control the supply of air under pressure to the said cylinder to urge the said piston in one direction; a relatively small displacement air cylinder and a piston movable therein and coupled to the first mentioned piston; means for continuously applying air pressure to the last mentioned piston so as to exert a force on the first mentioned piston in a direction opposite to the said one direction; a relatively large displacement hydraulic cylinder and a piston movable therein; an inlet valve arranged to admit hydraulic fluid to said large displacement cylinder; a relief valve arranged to be loaded in accordance with the available air supply pressure to open when the loading pressure is exceeded within the said relatively large displacement hydraulic cylinder; a relatively small displacement hydraulic cylinder connected to receive hydraulic fluid from the relatively large displacement hydraulic cylinder and to deliver hydraulic fluid to an outlet connection, the said pistons being mechanically connected so that when the relatively large displacement air piston is moved in the said one direction hydraulic fluid is drawn into the relatively large displacement hydraulic cylinder and delivered from the relatively small displacement hydraulic cylinder and the said inlet and exhaust valve mechanism being arranged to open an air inlet valve and close an exhaust valve when the piston in the relatively large displacement air cylinder has reached an end position under the action of the force exerted on the piston in the relatively small displacement air cylinder and to close the said inlet valve and open the said exhaust valve when the said piston reaches an opposite end position in the relatively large displacement air cylinder.

2. An air operated hydraulic pump comprising; a relatively large diameter air cylinder and a piston movable therein; inlet and exhaust valve mechanism arranged to control the supply of air under pressure to the said cylinder to urge the said piston in one direction; a relatively small diameter air cylinder and a piston movable therein and coupled to the first mentioned piston; means for continuously applying air pressure to the last mentioned piston so as to exert a force on the first mentioned piston in a direction opposite to the said one direction; a relatively large diameter hydraulic cylinder and a piston movable therein; an inlet valve arranged to admit hydraulic fluid to said large diameter cylinder; a-relief valve arranged to be loaded in accordance with the available air supply pressure to open when the loading pressure is exceeded within the said relatively large diameter hydraulic cylinder; a relatively small diameter hydraulic cylinder connected to receive hydraulic fluid from the relatively large diameter hydraulic cylinder and to deliver hydraulic fluid to an outlet connection, the said pistons being mechanically connected so that when the relatively large diameter air piston is moved in the said one direction hydraulic fluid is drawn into the relatively large diameter hydraulic cylinder and delivered from the relatively small diameter hydraulic cylinder and the said inlet and exhaust valve mechanisms being arranged to open an air inlet valve and close an exhaust valve when the piston in the relatively large diameter air cylinder has reached an edn position under the action of the force exerted on the piston in the relatively small diameter air cylinder and to close the said inlet valve and open the said exhaust valve when the said piston reaches an opposite end position in the relatively large diameter air cylinder.

3. An air operated hydraulic pump in accordance with claim 2, in which the said cylinders are coaxial and the said pistons are disposed upon a common piston rod.

4. An air operated hydraulic pump in accordance with claim 3, in which the means whereby the relatively small diameter hydraulic cylinder is connected to receive hydraulic fluid from the relatively large diameter hydraulic cylinder comprises the said common piston rod which is formed hollow to provide this facility. 

1. An air operAted hydraulic pump comprising: a relatively large displacement air cylinder and a piston movable therein; inlet and exhaust valve mechanism arranged to control the supply of air under pressure to the said cylinder to urge the said piston in one direction; a relatively small displacement air cylinder and a piston movable therein and coupled to the first mentioned piston; means for continuously applying air pressure to the last mentioned piston so as to exert a force on the first mentioned piston in a direction opposite to the said one direction; a relatively large displacement hydraulic cylinder and a piston movable therein; an inlet valve arranged to admit hydraulic fluid to said large displacement cylinder; a relief valve arranged to be loaded in accordance with the available air supply pressure to open when the loading pressure is exceeded within the said relatively large displacement hydraulic cylinder; a relatively small displacement hydraulic cylinder connected to receive hydraulic fluid from the relatively large displacement hydraulic cylinder and to deliver hydraulic fluid to an outlet connection, the said pistons being mechanically connected so that when the relatively large displacement air piston is moved in the said one direction hydraulic fluid is drawn into the relatively large displacement hydraulic cylinder and delivered from the relatively small displacement hydraulic cylinder and the said inlet and exhaust valve mechanism being arranged to open an air inlet valve and close an exhaust valve when the piston in the relatively large displacement air cylinder has reached an end position under the action of the force exerted on the piston in the relatively small displacement air cylinder and to close the said inlet valve and open the said exhaust valve when the said piston reaches an opposite end position in the relatively large displacement air cylinder.
 2. An air operated hydraulic pump comprising; a relatively large diameter air cylinder and a piston movable therein; inlet and exhaust valve mechanism arranged to control the supply of air under pressure to the said cylinder to urge the said piston in one direction; a relatively small diameter air cylinder and a piston movable therein and coupled to the first mentioned piston; means for continuously applying air pressure to the last mentioned piston so as to exert a force on the first mentioned piston in a direction opposite to the said one direction; a relatively large diameter hydraulic cylinder and a piston movable therein; an inlet valve arranged to admit hydraulic fluid to said large diameter cylinder; a relief valve arranged to be loaded in accordance with the available air supply pressure to open when the loading pressure is exceeded within the said relatively large diameter hydraulic cylinder; a relatively small diameter hydraulic cylinder connected to receive hydraulic fluid from the relatively large diameter hydraulic cylinder and to deliver hydraulic fluid to an outlet connection, the said pistons being mechanically connected so that when the relatively large diameter air piston is moved in the said one direction hydraulic fluid is drawn into the relatively large diameter hydraulic cylinder and delivered from the relatively small diameter hydraulic cylinder and the said inlet and exhaust valve mechanisms being arranged to open an air inlet valve and close an exhaust valve when the piston in the relatively large diameter air cylinder has reached an edn position under the action of the force exerted on the piston in the relatively small diameter air cylinder and to close the said inlet valve and open the said exhaust valve when the said piston reaches an opposite end position in the relatively large diameter air cylinder.
 3. An air operated hydraulic pump in accordance with claim 2, in which the said cylinders are coaxial and the said pistons are disposed upon a common piston rod.
 4. An air operated hydraulic pump in accordance with claim 3, in which the means whereby the relatively small diameteR hydraulic cylinder is connected to receive hydraulic fluid from the relatively large diameter hydraulic cylinder comprises the said common piston rod which is formed hollow to provide this facility. 